Spatiotemporally resolved far-field pulse contrast measuring method and device

1. A spatiotemporally resolved far-field pulse contrast measuring method, comprising steps of: (1) focusing an under-test beam in x dimension to make a focus of the under-test beam fall onto a front surface of a nonlinear correlation crystal; (2) making a spatial correlation and a temporal correlation respectively in two transverse spatial dimensions (x y) of the nonlinear correlation crystal by the far-field under-test beam and a sampling beam, so as to generate a two-dimensional correlating signal; (3) imaging the two-dimensional correlating signal onto a detection surface of a receiver system; and (4) detecting the two-dimensional correlating signal by the receiver system in a high sensitivity, and obtaining a spatiotemporal distribution of an under-test pulse contrast; wherein: the x dimension is a spatial dimension where noise has a spatiotemporal-coupling characterization; the x dimension is one of the two spatial dimensions when the noise has the spatiotemporal-coupling characterization in two spatial dimensions; and the under-test beam is focused in the y dimension to measure the far-field spatial distribution of noise in the y dimension.

2. The method, as recited in claim 1 , wherein the sampling beam on the surface of the nonlinear correlation crystal is shaped as a large spot or a focal spot; when the sampling beam is shaped as a focal spot, the sampling beam has the same focusing direction with the under-test beam.

3. The method, as recited in claim 1 , wherein the under-test beam and the sampling beam make a non-collinear cross-correlation in the y dimension to realize a single-shot temporal measurement; and, the under-test beam and the sampling beam make the spatial correlation in the x dimension in a single-shot mode or a scanning mode according to the sampling beam shaped as a large spot or a focused spot on the surface of the nonlinear correlation crystal.

4. A far-field pulse contrast single-shot measuring device of the method; as recited in claim 1 , comprising: a plano-convex cylindrical lens ( 3 ), a correlation crystal ( 4 ), a plano-convex imaging lens ( 8 ) and a signal-receiving system, wherein the signal-receiving system comprises a fiber array ( 9 ), a photomultiplier ( 13 ) and a digital oscilloscope ( 14 ); the fiber array ( 9 ) comprises N fiber-channels ( 10 ), attenuators ( 11 ) on each fiber channel ( 10 ) and a fiber bundle ( 12 ); a length of each fiber channel ( 10 ) between the fiber array ( 9 ) and the fiber bundle ( 12 ) increases successively from side to side with an incremental length of L meters; the correlation crystal ( 4 ) is located both at a focal plane of the plano-convex cylindrical lens ( 3 ) and an object plane of the plano-convex imaging lens ( 8 ); the fiber array ( 9 ) is located at an image plane of the plano-convex imaging lens ( 8 ); a line array of the fiber channels ( 10 ) is parallel with a focal line of the plano-convex imaging lens ( 3 ); wherein an output end of the photomultiplier ( 13 ) is connected with an input end of the digital oscilloscope ( 14 ).

5. The device, as recited in claim 4 , wherein the fibers are communication fibers or ultraviolet fibers according to signal wavelength; the fiber array ( 9 ) is fixed on a holder which is translational in the x dimension; the incremental length L of the fiber channels ( 10 ) is 1-2 meters and the number N of the fiber channels ( 10 ) is 50-200.

6. The device, as recited in claim 4 , wherein the fiber array ( 9 ) translates the received y-dimensional correlating signal ( 7 ) into a serial temporal pulse sequence, which is received and analyzed by the photomultiplier ( 13 ) and the oscilloscope ( 14 ).

7. An online identification method for origins of spatiotemporal noise of the device as recited in claim 4 , comprising steps of: when the fiber array ( 9 ) is located at a certain spatial position, displaying an image by the digital oscilloscope ( 14 ); placing a lens tissue in front of an optical surface to interfere a laser beam on the optical surface, and displaying by the digital oscilloscope ( 14 ) that a signal peak is typically enhanced, wherein the enhanced signal peak is just induced by optical surface.